The present invention relates to dilation catheters, and is directed more particularly to a dilation catheter which allows blood to flow thereby while it is being used to perform an angioplasty procedure.
The use of angioplasty to treat patients having stenoses, i.e., regions of constricted blood flow, in coronary arteries has become a widely accepted alternative to more invasive treatments. With this procedure the balloon of a dilation catheter is maneuvered into position across a stenoses, inflated to increase the size of the blood flow passage therethrough, and then deflated and withdrawn. In many cases this procedure has been found to produce a lasting increase in the rate of blood flow through the region of the stenoses thereby eliminating the need for coronary bypass surgery.
In many cases the angioplasty procedure must be performed on a succession of stenoses having different locations and sizes, necessitating the use of dilation catheters having different balloon sizes. In other cases it has been found that the proper treatment of a stenoses requires the application thereto of a succession of dilation balloons of progressively increasing size. Because the insertion of a dilation catheter into the body of a patient and the subsequent maneuvering thereof unavoidably presents some risk of injuring the walls of the patient's blood vessels, dilation catheters are used in conjunction with a guiding catheter which remains inside the patient throughout the procedure and which serves to protect the blood vessels from abrasion as successive dilation catheters are inserted and withdrawn.
Dilation catheters are also used in conjunction with a guidewire which, like the guiding catheter, remains within the patient when the dilation catheter is removed and replaced. This guidewire not only serves as a track or guide for the dilation catheter while it is inside of the guiding catheter, it also facilitates the final positioning of the balloon at a stenosis after the dilation catheter emerges from the end of the guiding catheter. Dilation catheters which may be exchanged without the removal and reinsertion of the guidewire are said to have a "rapid exchange capability". Examples of dilation catheters having such a rapid exchange capability are shown and described in U.S. Pat. Nos. 4,762,129 (Bonzel) and 5,061,273 (Yock).
In most cases the full benefit of the angioplasty procedure will not be realized if the dilation balloon is deflated immediately after being inflated. This is because it takes time for the material making up the stenoses to reconfigure itself and become consolidated into a mass that will not readily return to its original flow constricting shape. As a result, the balloon may have to be maintained in its inflated state for many seconds. This can result in a serious risk to the patient because, unless special provision is made for the perfusion of blood thereby, an inflated dilation balloon will stop the flow of blood through the vessel in which it is located. Dilation catheters which make provision for the perfusion of blood are said to have a "perfusion capability". Examples of dilation catheters having such a perfusion capability are shown and described in U.S. Pat. Nos. 4,763,654 (Jang) and 4,983,167 (Sahota).
The dilation balloons of dilation catheters are ordinarily of one of two types. A first of these types includes balloons which are distributed more or less symmetrically with respect to the associated guidewires. Examples of dilation catheters which include balloons of this type and which have a rapid exchange capability include the previously cited Bonzel and Yock patents. Examples of dilation catheters which include balloons of this type, but which do not have a rapid exchange capability, are described in U.S. Pat. Nos. 4,323,071 (Simpson et.al.) and 4,195,637 (Gruntzig et.al.). Dilation catheters having balloons of this type have the advantage that they act on a stenosis uniformly in all directions, but have the disadvantage that they are unable to present the stenosis with a surface that is relatively stiff, i.e., unyielding. Such a surface can be beneficial in the case of stenoses that are relatively hard and need to be, in effect, "cracked" open.
A second of these types includes balloons which are offset to one side of the associated guidewire. Examples of dilation catheters which include one or more balloons of this type are described in U.S. Pat. Nos. 5,071,406 (Jang) and 5,304,132 (Jang), neither catheter having either a rapid exchange capability or a perfusion capability. One advantage of dilation catheters having balloons of this type is that they are able to present at least part of a stenosis with a relatively stiff surface. Another advantage is that their lack of symmetry enables them to be oriented for use in treating stenoses that are distributed unsymmetrically within a blood vessel.
In view of the foregoing it will be seen that, prior to the present invention, there has not been available a dilation catheter which has both a rapid exchange capability and a perfusion capability, and yet which has all of the advantages of dilation catheters that include offset balloons.